Electrophotographic image-forming machines are used to transfer images onto paper or other medium in both printing and facsimile systems. Generally, a photoconductor is selectively charged and optically exposed to form an electrostatic latent image on the surface. Toner is deposited onto the charged photoconductor surface. The toner has a charge, thus it will adhere to the photoconductor surface in areas corresponding to the electrostatic latent image. The toner image is transferred to the paper or other medium. The toned paper is heated by a fuser roller system for the toner to fuse to the paper. The photoconductor is then refreshed—cleaned to remove any residual toner and charge—to make it ready for another image. The imaged paper is then passed to a document output collection area or tray where the user collects the finished, permanently imaged paper or documents.
The fuser rolls used in these image-forming systems are usually driven by a keyed hub that rides in a slot at the end of the fuser roll. The key drives the fuser roll which is made up of an aluminum core and a coating such as Teflon® (a trademark of DuPont); sometimes a small stainless steel limit stop is attached to the slot. When the key drives the fuser roll, it transfers the load to the fuser roll core causing it to rotate. Cracks forming after extended use in the fuser roll have been frequently experienced which eventually reduces the useful fuser roll life and requires replacement. After some investigation, it has been found that this cracking initially occurs in the upper region of the drive slot primarily because of the substantial load transferred to the fuser core slot during rotation and subsequent frequent braking of the fuser roll.
This cracking at the fuser roll slot which occurs in all sizes of fuser rolls has become a significant problem and results in frequent fuser roll replacement. It is not uncommon for fuser rolls to be recoated with Teflon® (or other coating) after the initial coating is worn or damaged. Sometimes this coating is replaced on the same fuser roll core two or three times. Extending the useful life of the relatively expensive core has become a high priority since cost effectiveness is always a concern. The load placed on the slot by the drive key with sudden stopping of the rotation plus the sometimes high temperatures used during fusing have accelerated the formation of cracks and deterioration of the core around the slot. Also it has been determined that the relatively small dimensions of the prior art slots in fuser rolls makes the cracks caused by stress more likely to occur.